Load balancing logical units in an active/passive storage system

ABSTRACT

An approach is provided in which a storage system includes a first storage controller, a second storage controller, and multiple logical units. The storage system determines that a controller traffic load ratio between the first storage controller and the second storage controller has reached a threshold. In turn, the storage system selects one of the logical units and changes a preferred controller ownership of the selected logical unit from the first storage controller to the second storage controller to balance the controller traffic load ratio.

BACKGROUND

The present disclosure relates to load balancing logical units in an active/passive storage system. More particularly, the present disclosure relates to dynamically updating preferred controller ownership of logical units to balance data traffic loads passing through the storage controllers.

A storage area network (SAN) is a dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to make storage resources (e.g., disk arrays, tape libraries, optical jukeboxes, etc.) accessible to servers such that the resources appear as locally attached devices to the operating system.

A SAN typically includes file systems, which are logical storage abstraction mappings to the physical storage resources (storage virtualization). In a block-based storage environment, a single block of information is addressed using a logical unit (LUN) identifier and an offset within that LUN—known as a logical block addressing (LBA). The LUN identifier identifies a logical unit from multiple LUNs and is essential for managing block storage arrays of a storage area network (SAN). A typical LUN may be used with any storage resource that supports read/write processes.

A SAN may include several storage controllers that interface host systems to the LUNs. Multi-controller storage systems may be configured in an active/active configuration or an active/passive configuration. In an active/passive configuration, the SAN specifies a “preferred controller” for each logical unit. As such, a host operating system uses the preferred controller to access a particular logical unit as long as the controller is available. When the preferred controller is unavailable (e.g., network connection issue, device issue, etc.), the host operating system accesses the SAN's other storage controller.

BRIEF SUMMARY

According to one embodiment of the present disclosure, an approach is provided in which a storage system includes a first storage controller, a second storage controller, and multiple logical units. The storage system detects that a controller traffic load ratio between the first storage controller and the second storage controller has reached a threshold. The storage system, in turn, selects one of the logical units and changes a preferred controller ownership of the selected logical unit from the first storage controller to the second storage controller to balance the controller traffic load ratio.

The foregoing is a summary and thus contains, by necessity, simplifications, generalizations, and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the present disclosure, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth below.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present disclosure may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings, wherein:

FIG. 1 is a diagram showing an example of a storage system dynamically adjusting preferred controller logical unit ownership based upon logical unit traffic loads at the storage controllers;

FIG. 2A is a diagram showing an example of an ownership configuration user interface on which an administrator selects an ownership configuration;

FIG. 2B shows an example of a logical unit ownership table managed by storage system 100;

FIGS. 3A and 3B are diagrams showing an example of a storage system changing preferred controller ownership when a controller traffic load ratio reaches an auto-balance threshold;

FIG. 4 is a diagram showing one example of a host system sending an inquiry to a storage system prior to accessing a logical unit through a storage controller;

FIG. 5 is a flowchart showing one example of steps taken by a storage system to manage logical unit data traffic load balancing between storage controllers;

FIG. 6 is a flowchart showing one example of steps taken by a host system to send/receive data to/from logical units through selected storage controllers;

FIG. 7 is diagram showing an example of a graphical representation a storage system maintaining a balanced traffic load between two storage controllers by dynamically adjusting preferred controller ownership of logical units within the storage system;

FIG. 8 is a block diagram of a data processing system in which the methods described herein can be implemented; and

FIG. 9 provides an extension of the information handling system environment shown in FIG. 8 to illustrate that the methods described herein can be performed on a wide variety of information handling systems which operate in a networked environment.

DETAILED DESCRIPTION

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.

As will be appreciated by one skilled in the art, aspects of the present disclosure may be embodied as a system, method or computer program product. Accordingly, aspects of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

Computer program code for carrying out operations for aspects of the present disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Aspects of the present disclosure are described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

The following detailed description will generally follow the summary of the disclosure, as set forth above, further explaining and expanding the definitions of the various aspects and embodiments of the disclosure as necessary.

FIG. 1 is a diagram showing an example of a storage system dynamically adjusting preferred controller logical unit ownership based upon logical unit traffic loads at the storage controllers. Storage system 100 (e.g., a storage area network) includes logical units 120, 125, and 130, which provide a logical storage abstraction of physical storages 170-190 to hosts 140 and 150. In one embodiment, physical storages 170-190 are aggregated into storage pools from which the logical storage is created. Such storage virtualization helps achieve location independence by abstracting the physical location of the data. As such, system 100 presents to hosts 140 and 150 a logical space for data storage and handles the process of mapping the data to the actual physical location (physical storage 170-190).

Storage controllers 105 and 110, in one embodiment, manage data traffic between logical units 120-130 and hosts 140-150 in an active/passive configuration. Those skilled in the art understand that, in an active/passive configuration, each logical unit has an assigned preferred controller and an assigned current controller. A particular logical unit's preferred controller is the controller a host should use when the host unit accesses the logical unit. A logical unit's current controller is the controller temporarily utilized by a host when the host is unable to access the logical unit via the preferred controller (e.g., network connection issues, controller issues, etc.).

Storage system 100 may initially configure preferred controller logical unit ownership according to default parameters, such as assigning half of the logical units to storage controller 105 and the other half of the logical units to the storage controller 110. Storage system 100 uses logical unit (LUN) ownership table 115 to track logical unit controller ownership information via preferred controller identifiers and current controller identifiers (see FIG. 2B and corresponding text for further details). FIG. 1 shows that storage controller 1 105 is the designated preferred controller for logical unit A 120 and logical unit B 125 (solid lines), and storage controller 2 110 is the designated preferred controller for logical unit C 130. The dashed lines shown in FIG. 1 represent storage system's active/passive configuration in that preferred controller ownership may be dynamically updated to balance data traffic loads between storage controller 1 105 and storage controller 2 110.

When host 140 receives a request from an application to access data, host 140 identifies a corresponding logical unit and sends an inquiry to storage system 100 to receive information (stored in LUN ownership table 115) as to the logical unit's preferred controller. In turn, host 140 stores the preferred controller information in local table 145 and begins accessing the logical unit through the preferred controller. For example, host 140 may receive a request to access data on logical unit A 120 and, in this example, determines that storage controller 1 105 is the preferred controller (from storage system 100's response, see FIG. 4 and corresponding text for further details).

As network activity increases, storage system 100 monitors the “controller traffic load ratio” between logical unit data traffic passing through storage controller 1 105 and storage controller 2 110. When storage system 100 detects an unbalanced amount of traffic passing through one storage controller compared to the other storage controller, storage system 100 dynamically changes the preferred controller ownership of one or more of the logical units via logical unit ownership table 115, such as changing the preferred controller of logical unit B 125 from storage controller 1 105 to storage controller 2 110 (see FIGS. 3A, 3B, and corresponding text for further details).

In turn, when host 140 or host 150 sends an inquiry to storage system 100 that inquires about logical unit B 125's preferred controller, storage system 100 sends a response that identifies storage controller 2 110 as the new preferred controller. As such, host 140 and host 150 update their local tables 145 and 155, respectively, and access logical unit B 125 through storage controller 110 to balance the data traffic passing through the two different storage controllers.

FIG. 2A is a diagram showing an example of an ownership configuration user interface on which an administrator selects an ownership configuration. In one embodiment, storage system 100 displays window 200 to an administrator, which allows the administrator to select between a dynamic ownership configuration (automatically adjust preferred controller logical unit ownership), or a static ownership configuration (fixed preferred controller logical unit ownership).

Window 200 shows that an administration selects box 210 to configure storage system 100 in a dynamic ownership configuration. In addition, the administrator enters an auto-balance threshold in box 215, which triggers storage system 100 to adjust preferred controller ownership when the controller traffic load ratio reaches the entered auto-balance threshold. The example in FIG. 2A shows a value of +/−10%, which indicates that storage controller 100 adjusts the preferred controller ownership when the data traffic passing through one storage controller is +/−10% more/less than the data traffic passing through the other storage controller (see FIG. 7 and corresponding text for further details).

The administrator selects box 220 to configure storage system 100 in a static ownership configuration. When the administrator selects box 220, the administrator also enters logical unit identifiers in boxes 225 and storage controller identifiers in box 230, which set the storage controllers as the preferred controllers of the corresponding logical units. As those skilled in the art can appreciate, although storage system 100 may change the current controller identifiers of logical units in the static ownership configuration (based on network connection issues, device issues, etc.), storage system 100 does not changes the preferred controller identifiers in the static ownership configuration.

FIG. 2B shows an example of a logical unit ownership table managed by storage system 100. Logical unit ownership table 115 includes logical unit identifiers (column 240), preferred controller identifiers (column 250), and current controller identifiers (column 260). As can be seen, storage controller 1 105 is the preferred controller for logical unit A, whereas storage controller 2 110 is the preferred controller for logical units B and C. Logical unit ownership table 115 also shows that logical unit B's current controller is storage controller 1 105. This may be due to a host system not being able to access logical unit B through storage controller 2 110, in which case the host system sends a notice to storage system 100, which changes the current controller from storage controller 2 110 (matching the preferred controller) to storage controller 1 105 (see FIG. 6 and corresponding text for further details).

FIGS. 3A and 3B are diagrams showing an example of a storage system changing preferred controller ownership when a controller traffic load ratio reaches an auto-balance threshold. Referring to FIG. 3A, storage system 100's ownership table 115 shows that storage controller 1 105 is the preferred controller for logical unit A 120 and logical unit B 125, and storage controller 2 110 is the preferred controller for logical unit C 130. During operation, storage system 100 monitors the relative amount of data traffic through storage controller 1 105 and storage controller 2 110, which is referred to herein as the controller traffic load ratio. When the amount of data traffic through storage controller 1 105 becomes disproportionate to the amount of data traffic through storage controller 2 110 (e.g., reaches an auto-balance threshold), storage system 100 changes preferred controller ownership of one or more of the logical units to balance the data traffic through the storage controllers (see FIG. 3B and corresponding text for further details).

FIG. 3B shows that, compared to FIG. 3A, storage system 100 changed logical unit B 125's preferred controller ownership and current controller from storage controller 1 105 to storage controller 2 110 (shown in logical unit ownership table 115). As such, when a host system sends an ownership inquiry to storage system 110, storage system 110 sends the updated preferred controller ownership/current controller information and, in turn, the inquiring host accesses logical unit B 125 through storage controller 2 110.

FIG. 4 is a diagram showing one example of a host system sending an inquiry to a storage system prior to accessing a logical unit through a storage controller. Host 140 sends inquiry 400 to storage system 100, which inquires about the ownership of a particular logical unit (identified by LUN ID in inquiry 400). Storage system 100, in turn, access LUN ownership table 115 and retrieves the preferred controller ID and the current controller ID corresponding to the logical unit identified in inquiry 400. Storage system 100 sends ownership response 410 back to host 140, which includes the LUN ID, the preferred controller ID, and the current controller ID. Host 140, in turn, updates local table 145 with the ownership information and proceeds to access the logical unit via the identified preferred storage controller (see FIG. 6 and corresponding text for further details).

FIG. 5 is a flowchart showing one example of steps taken by a storage system to manage logical unit data traffic load balancing between storage controllers. Processing commences at 500, whereupon the storage system provides a configuration user interface (e.g., window 200 shown in FIG. 2A) to a user and receives an ownership configuration selection from the user (505). A determination is made as to whether the ownership configuration selection is a static configuration selection or a dynamic configuration selection (decision 510). If the user selects a static ownership configuration, decision 510 branches to the “static” branch, whereupon the storage system populates logical unit ownership table 115 with static ownership preferences included in the user's response and preferred controller ownership management ends at 520. As those skilled in the art can appreciate, storage system 100 may update the current controller information in a static ownership configuration, but the preferred controller ownership remains fixed.

On the other hand, if the user selects a dynamic ownership configuration, decision 510 branches to the “dynamic” branch, whereupon the storage system populates logical unit ownership table 115 with default ownership preferences at 525. For example, the storage system may assign the first half of logical units (e.g., 1-3) to the first storage controller and assign the second half of logical units (e.g., 4-6) to the second storage controller.

At 530, the storage system monitors input/output loads of the storage controllers (data traffic load) and computes a controller traffic load ratio. In one embodiment, the storage system may use a total number of bytes transferred within a given time period (e.g., within the last minute). In this embodiment, if controller 1 owns LUN A and LUN B, and controller 2 owns LUN C, then the controller traffic load ratio is “traffic on LUN A+traffic on LUN B:traffic on LUN C”.

A determination is made as to whether the controller traffic load ratio exceeds an auto-balance threshold (decision 540). In one embodiment, the user provides the auto-balance threshold (e.g., +/−10%), such as threshold 215 shown in FIG. 2A. If the controller traffic load ratio does not exceed the auto-balance threshold, decision 540 branches to the “No” branch, which loops back to continue to monitor the data traffic loads on each storage controller.

On the other hand, if the controller traffic load ratio reaches the auto-balance threshold, decision 540 branches to the “Yes” branch, whereupon the storage system updates the preferred controller/current controller ownership of one or more logical units accordingly to balance the traffic load between controllers. For example, the storage system may partition the LUNs into different groups and identify a particular partition that provides the optimum controller traffic load ratio (e.g., closest to a value of “1”).

A determination is made as to whether to continuing monitoring the data traffic loads on the storage controllers (decision 560). If the storage system should continue to monitor data traffic loads, decision 560 branches to the “Yes” branch, which loops back to dynamically adjust preferred controller ownership based upon load conditions. On the other hand, if the storage controller should stop monitoring load conditions, decision 560 branches to the “No” branch, whereupon processing ends at 570.

FIG. 6 is a flowchart showing one example of steps taken by a host system to send/receive data to/from logical units through selected storage controllers. Processing commences at 600, whereupon the host system receives a request from application 605 to send/receive data at 610.

The host system identifies the logical unit associated with the request (via from application 605 or file system) and accesses local table 145 to identify the current controller of the identified logical unit (620). Local table 145 includes ownership information based upon the host system's last interaction with storage system 100. The host system sends a request to the identified current controller to send/retrieve data to/from a particular LUN (630).

A determination is made as to whether the host system received a response from storage system 100 (decision 640). When a connection between the host system and storage system 100 is functioning correctly, storage system 100 receives the request and provides either a valid response or an error response to the host system that indicates the controller, which the host thought was the current controller, is actually not the current controller of the requested LUN. However, when the connection is not functioning properly (transmit path down, receive path down, storage controller non-functional, etc.), the host system does not receive a response.

If the host system receives a valid response, decision 640 branches to the “Valid” branch whereupon the host system sends/receives data to/from the LUN through the current controller (660). On the other hand, if the host received an error message, decision 640 branches to the “Error” branch whereupon the host changes the current controller of the LUN in local table 145 (e.g., controller 1 to controller 2) at 655, and sends/receives data to/from the LUN through the new current controller (660).

However, if the host does not receive a response from storage system 100, decision 640 branches to the “None” branch, whereupon the host changes the current controller of the LUN in local table 145 (e.g., controller 1 to controller 2) at 650, and sends a notice to storage system 100 of the change in current controller at 655. In one embodiment, storage system 100 updates the current controller of the LUN in LUN ownership table 115 when it receives the notice from the host system. The host then sends/receives data to/from the LUN through the new current controller (660).

A determination is made on whether to continue processing requests from applications such as application 605 (decision 670). If host processing should continue, decision 670 branches to the “Yes” branch, whereupon the host system receives and processes application requests. This looping continues until host processing should terminate, at which point decision 670 branches to the “No” branch, whereupon processing ends at 680.

FIG. 7 is diagram showing an example of a graphical representation a storage system maintaining a balanced traffic load between two storage controllers by dynamically adjusting preferred controller ownership of logical units within the storage system.

Graph 700 shows a relative logical unit traffic load (controller traffic load ratio 710) over time between two storage controllers. At time t0, the relative logical unit traffic load is balanced between storage controller 1 105 and storage controller 2 110. For example, storage system 100 may split the amount of preferred controller ownerships between the two different storage controllers when storage system 100 boots up (e.g., 525 in FIG. 5).

As time progress toward time t1, the amount of logical unit traffic increases through storage controller 1 105 relative to the amount of logical unit traffic through storage controller 2 110, hence controller traffic load ratio 710 has a positive slope. At time t1, controller traffic load ratio 710 reaches auto-balance threshold 720, which may be set by a system administrator through a user interface, such as window 200 shown in FIG. 2A. As such, storage system 100 changes the preferred controller ownership of one or more logical units in order to move some of the logical unit traffic from storage controller 1 105 to storage controller 2 110. As shown in FIGS. 3A and 3B, storage system 100 changes the preferred controller ownership of a logical unit by changing the corresponding preferred controller identifier in logical unit ownership table 115. In turn, when a host system sends an ownership inquiry to storage system 100, storage system 100 sends a response with the updated preferred controller information.

As storage system 100 moves preferred controller ownership of one or more logical units from storage controller 1 105 to storage controller 2 110, the host systems begin to pass more logical unit data traffic through storage controller 2 110. In turn, logical unit traffic ratio 710 balances between storage controller 1 105 and storage controller 2 110. As time progresses to time t2, controller traffic load ratio 710 reaches auto-balance threshold 730. For example, assuming that a controller traffic load ratio during a balanced load is “0,” thresholds 720 and 730 may be +10% and −10%, respectively (or 0.10 and −0.10).

At time t2, storage system 100 changes the preferred controller ownership of one or more logical units in order to move some of the logical unit traffic from storage controller 2 110 to storage controller 1 105 by changing the corresponding preferred controller identifier in logical unit ownership table 115. By dynamically re-assigning preferred controller ownership of the logical units, the traffic load passed through the storage controllers remains balanced and, in turn, bottlenecks are reduced.

FIG. 8 illustrates information handling system 800, which is a simplified example of a computer system capable of performing the computing operations described herein. Information handling system 800 includes one or more processors 810 coupled to processor interface bus 812. Processor interface bus 812 connects processors 810 to Northbridge 815, which is also known as the Memory Controller Hub (MCH). Northbridge 815 connects to system memory 820 and provides a means for processor(s) 810 to access the system memory. Graphics controller 825 also connects to Northbridge 815. In one embodiment, PCI Express bus 818 connects Northbridge 815 to graphics controller 825. Graphics controller 825 connects to display device 830, such as a computer monitor.

Northbridge 815 and Southbridge 835 connect to each other using bus 819. In one embodiment, the bus is a Direct Media Interface (DMI) bus that transfers data at high speeds in each direction between Northbridge 815 and Southbridge 835. In another embodiment, a Peripheral Component Interconnect (PCI) bus connects the Northbridge and the Southbridge. Southbridge 835, also known as the I/O Controller Hub (ICH) is a chip that generally implements capabilities that operate at slower speeds than the capabilities provided by the Northbridge. Southbridge 835 typically provides various busses used to connect various components. These busses include, for example, PCI and PCI Express busses, an ISA bus, a System Management Bus (SMBus or SMB), and/or a Low Pin Count (LPC) bus. The LPC bus often connects low-bandwidth devices, such as boot ROM 896 and “legacy” I/O devices (using a “super I/O” chip). The “legacy” I/O devices (898) can include, for example, serial and parallel ports, keyboard, mouse, and/or a floppy disk controller. The LPC bus also connects Southbridge 835 to Trusted Platform Module (TPM) 895. Other components often included in Southbridge 835 include a Direct Memory Access (DMA) controller, a Programmable Interrupt Controller (PIC), and a storage device controller, which connects Southbridge 835 to nonvolatile storage device 885, such as a hard disk drive, using bus 884.

ExpressCard 855 is a slot that connects hot-pluggable devices to the information handling system. ExpressCard 855 supports both PCI Express and USB connectivity as it connects to Southbridge 835 using both the Universal Serial Bus (USB) the PCI Express bus. Southbridge 835 includes USB Controller 840 that provides USB connectivity to devices that connect to the USB. These devices include webcam (camera) 850, infrared (IR) receiver 848, keyboard and trackpad 844, and Bluetooth device 846, which provides for wireless personal area networks (PANs). USB Controller 840 also provides USB connectivity to other miscellaneous USB connected devices 842, such as a mouse, removable nonvolatile storage device 845, modems, network cards, ISDN connectors, fax, printers, USB hubs, and many other types of USB connected devices. While removable nonvolatile storage device 845 is shown as a USB-connected device, removable nonvolatile storage device 845 could be connected using a different interface, such as a Firewire interface, etcetera.

Wireless Local Area Network (LAN) device 875 connects to Southbridge 835 via the PCI or PCI Express bus 872. LAN device 875 typically implements one of the IEEE 802.11 standards of over-the-air modulation techniques that all use the same protocol to wireless communicate between information handling system 800 and another computer system or device. Optical storage device 890 connects to Southbridge 835 using Serial ATA (SATA) bus 888. Serial ATA adapters and devices communicate over a high-speed serial link. The Serial ATA bus also connects Southbridge 835 to other forms of storage devices, such as hard disk drives. Audio circuitry 860, such as a sound card, connects to Southbridge 835 via bus 858. Audio circuitry 860 also provides functionality such as audio line-in and optical digital audio in port 862, optical digital output and headphone jack 864, internal speakers 866, and internal microphone 868. Ethernet controller 870 connects to Southbridge 835 using a bus, such as the PCI or PCI Express bus. Ethernet controller 870 connects information handling system 800 to a computer network, such as a Local Area Network (LAN), the Internet, and other public and private computer networks.

While FIG. 8 shows one information handling system, an information handling system may take many forms. For example, an information handling system may take the form of a desktop, server, portable, laptop, notebook, or other form factor computer or data processing system. In addition, an information handling system may take other form factors such as a personal digital assistant (PDA), a gaming device, ATM machine, a portable telephone device, a communication device or other devices that include a processor and memory.

The Trusted Platform Module (TPM 895) shown in FIG. 8 and described herein to provide security functions is but one example of a hardware security module (HSM). Therefore, the TPM described and claimed herein includes any type of HSM including, but not limited to, hardware security devices that conform to the Trusted Computing Groups (TCG) standard, and entitled “Trusted Platform Module (TPM) Specification Version 1.2.” The TPM is a hardware security subsystem that may be incorporated into any number of information handling systems, such as those outlined in FIG. 9.

FIG. 9 provides an extension of the information handling system environment shown in FIG. 8 to illustrate that the methods described herein can be performed on a wide variety of information handling systems that operate in a networked environment. Types of information handling systems range from small handheld devices, such as handheld computer/mobile telephone 910 to large mainframe systems, such as mainframe computer 970. Examples of handheld computer 910 include personal digital assistants (PDAs), personal entertainment devices, such as MP3 players, portable televisions, and compact disc players. Other examples of information handling systems include pen, or tablet, computer 920, laptop, or notebook, computer 930, workstation 940, personal computer system 950, and server 960. Other types of information handling systems that are not individually shown in FIG. 9 are represented by information handling system 980. As shown, the various information handling systems can be networked together using computer network 900. Types of computer network that can be used to interconnect the various information handling systems include Local Area Networks (LANs), Wireless Local Area Networks (WLANs), the Internet, the Public Switched Telephone Network (PSTN), other wireless networks, and any other network topology that can be used to interconnect the information handling systems. Many of the information handling systems include nonvolatile data stores, such as hard drives and/or nonvolatile memory. Some of the information handling systems shown in FIG. 9 depicts separate nonvolatile data stores (server 960 utilizes nonvolatile data store 965, mainframe computer 970 utilizes nonvolatile data store 975, and information handling system 980 utilizes nonvolatile data store 985). The nonvolatile data store can be a component that is external to the various information handling systems or can be internal to one of the information handling systems. In addition, removable nonvolatile storage device 845 can be shared among two or more information handling systems using various techniques, such as connecting the removable nonvolatile storage device 845 to a USB port or other connector of the information handling systems.

While particular embodiments of the present disclosure have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, that changes and modifications may be made without departing from this disclosure and its broader aspects. Therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this disclosure. Furthermore, it is to be understood that the disclosure is solely defined by the appended claims. It will be understood by those with skill in the art that if a specific number of an introduced claim element is intended, such intent will be explicitly recited in the claim, and in the absence of such recitation no such limitation is present. For non-limiting example, as an aid to understanding, the following appended claims contain usage of the introductory phrases “at least one” and “one or more” to introduce claim elements. However, the use of such phrases should not be construed to imply that the introduction of a claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to disclosures containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an”; the same holds true for the use in the claims of definite articles. 

The invention claimed is:
 1. An information handling system comprising: one or more processors; a memory coupled to at least one of the processors; a plurality of storage controllers; a plurality of logical units; and a set of computer program instructions stored in the memory and executed by at least one of the processors in order to perform actions of: determining that a controller traffic load ratio between a first storage controller and a second storage controller has reached a threshold, wherein the first storage controller and the second storage controller are included in the plurality of storage controllers and correspond to at least one of the plurality of logical units; changing, by the storage system, a preferred controller ownership corresponding to a selected one of the plurality of logical units from the first storage controller to the second storage controller in response to the determination; sending an error message to a host system upon receiving a request to the first storage controller to send or retrieve data to or from the selected logical unit, wherein the error message indicates that the first storage controller is not the current controller of the selected logical unit; receiving a second request to the second storage controller to send or retrieve data to or from the selected logical unit; and sending a valid response to the host system indicating that the host system may send and receive data to the selected logical unit through the second controller.
 2. The information handling system of claim 1 wherein the information handling system configures the first storage controller and the second storage controller in an active/passive controller configuration.
 3. The information handling system of claim 1 wherein, prior to the determination that the controller traffic load ratio has reached the threshold, the set of instructions, when executed by at least one of the processors, performs further actions of: identifying a first data traffic amount passing through the first storage controller corresponding to one or more first logical units included in the plurality of logical units; identifying a second data traffic amount passing through the second storage controller corresponding to one or more second logical units included in the plurality of logical units; and computing the controller traffic load ratio based upon the first data traffic amount and the second data traffic amount.
 4. The information handling system of claim 1 wherein the set of instructions, when executed by at least one of the processors, performs further actions of: displaying an ownership configuration window to a user; receiving an ownership configuration selection from the user; determining that the ownership configuration selection is a dynamic ownership selection; and configuring the information handling system to balance the controller traffic load ratio, wherein the balancing includes changing one or more preferred controller ownerships of one or more of the plurality of logical units when the controller traffic load ratio reaches the threshold.
 5. The information handling system of claim 4 wherein the threshold is an auto-balance threshold received from the user.
 6. The information handling system of claim 1 wherein each of the plurality of logical units corresponds to at least a portion of a physical storage device.
 7. A computer program product stored in a non-transitory computer readable storage medium, comprising computer program code that, when executed by an information handling system, causes the information handling system to perform actions comprising: determining that a controller traffic load ratio between a first storage controller and a second storage controller has reached a threshold, wherein the first storage controller and the second storage controller are included in the plurality of storage controllers and correspond to at least one of the plurality of logical units; changing, by the storage system, a preferred controller ownership corresponding to a selected one of the plurality of logical units from the first storage controller to the second storage controller in response to the determination; sending an error message to a host system upon receiving a request to the first storage controller to send or retrieve data to or from the selected logical unit, wherein the error message indicates that the first storage controller is not the current controller of the selected logical unit; receiving a second request to the second storage controller to send or retrieve data to or from the selected logical unit; and sending a valid response to the host system indicating that the host system may send and receive data to the selected logical unit through the second controller.
 8. The computer program product of claim 7 wherein the computer program code that, when executed by the information handling system, causes the information handling system to configure the first storage controller and the second storage controller in an active/passive controller configuration.
 9. The computer program product of claim 7 wherein the computer program code that, when executed by the information handling system, causes the information handling system to perform further actions of: identifying a first data traffic amount passing through the first storage controller corresponding to one or more first logical units included in the plurality of logical units and; identifying a second data traffic amount passing through the second storage controller corresponding to one or more second logical units included in the plurality of logical units; and computing the controller traffic load ratio based upon the first data traffic amount and the second data traffic amount.
 10. The computer program product of claim 7 wherein the computer program code that, when executed by the information handling system, causes the information handling system to perform further actions of: displaying an ownership configuration window to a user; receiving an ownership configuration selection from the user; determining that the ownership configuration selection is a dynamic ownership selection; and configuring the information handling system to balance the controller traffic load ratio, wherein the balancing includes changing one or more preferred controller ownerships of one or more of the plurality of logical units when the controller traffic load ratio reaches the threshold.
 11. The computer program product of claim 10 wherein the threshold is an auto-balance threshold received from the user. 